Question

why do veins have thin walls as compared to Atria​

Answer 1

Answer:

because in arteries blood goes in very tight pressure which cannot be imagined

Answer 2

Answer:

Blood through arteries flow at a high pressure due to pumping of blood by heart. There are chances for its walls to break or rupture due to too much hugh pressure. So, there is need of thick walls so as to prevent this.

Whereas, the opposite is the case in veins. The blood through veins flow at a pressure comparatively lower than arteries, as the blood from the rest of the body organs come with less pressure. Thus, there is no requirement of such thick walls.